The invention relates to a downhole pressure and vibration measuring device integrated in a pipe section as part of a production tubing, as defined in the introduction of the accompanying claim 1.
Downhole instrumentation is used to acquire measuring data in production wells and is an important tool for the optimal control of the production. The reliability of the downhole meters is poor in high temperatures, typically 110° C. or higher. A rule of thumb says that the error rate is doubled for every ten degrees' increase in temperature.
The reduced life of downhole instrumentation in oil and gas wells because of high temperatures is a large problem. In practice, the expenses of a well intervention are too large for malfunctioning downhole instrumentation to be replaced. This is true for subsea wells in particular. Over time, a loss of this instrumentation function may have economic consequences in that the control of the well is not optimal.
Modern measuring systems are typically silicone, sapphire or quartz sensors with electronics. A large number of downhole electronic measuring systems have been installed during the last twenty years, and many studies have been carried out to evaluate the reliability of this type of equipment. One evaluation revealed that only 88% of the installations were still functioning after four years in operation, and a trend showed a drop of 3% per year, indicating that ⅓ of the wells would have lost their downhole monitoring by the end of the well's life.
Other downhole measuring systems are optical-fibre measuring instruments, which can stand high temperatures but are attacked by hydrogen, which blackens the fibres. Measuring instruments with capillary tubes are used primarily for pressure measuring with inert gas, like nitrogen and helium, and in combinations with optical-fibre temperature measurement. Faults may arise by particles blocking bubble tubes, for example through gas leakages, and when pressure chambers are undersized, so that oil will enter gas tubes.
From the patent literature are cited as the background art:                U.S. Pat. No. 5,226,494 disclosing a downhole tool, in which strain gauges are to register applied forces to initiate a downhole function without using ports in the production tubing or the work string, a method being sought for the reliable activation of the function from the surface. Changes in signals from the strain gauges mounted on a tubular part included in the tool on mechanical influence may be recorded by downhole electronics, and when an activating sequence of influence is recognized, the electronics will release energy stored in the tool, which performs a desired tool function.        U.S. Pat. No. 6,384,738 disclosing an invention with the same object.        
The invention of the application is substantially different from the two mentioned above, with respect to object, embodiment as well as function.